Papers by Robert O Ritchie
Mechanical Behaviour of Materials at High Temperature
Springer eBooks, 1996
Page 1. v Mechanical Behaviour of Materials at High Temperature Edited by C. Moura Branco, R... more Page 1. v Mechanical Behaviour of Materials at High Temperature Edited by C. Moura Branco, R. Ritchie and V. Sklenifika NATO ASI Series 3. High Technology-Vol. 15 Page 2. Page 3. L; Q *.<* r; c: Page 4. Page 5. Page 6. Page 7. ...
Cryoforged nanotwinned titanium with ultrahigh strength and ductility
Science, Sep 17, 2021
Titanium gets some twins Introducing a network of nanotwins is known to improve the properties of... more Titanium gets some twins Introducing a network of nanotwins is known to improve the properties of face-centered cubic metal alloys. Zhao et al . used gentle compression in liquid nitrogen to introduce a similar network of nanotwins in hexagonal closed-packed titanium. By starting with a titanium that has little oxygen, the twin network can be more easily established. The nanotwinned network improved the yield strength by 50% and ductility by 20% at room temperature. The cryogenic properties were even better, with a yield strength of two gigapascals and a tensile ductility of 100% before failure. —BG
Phase transformations in an in situ Nb-reinforced Nb3Al intermetallic composite
Intermetallics, 1996
The development of two-phase Nb/Nb3Al in situ composite microstructures by thermal treatment in a... more The development of two-phase Nb/Nb3Al in situ composite microstructures by thermal treatment in a Nb-6wt. %Al alloy, processed through powder-metallurgy techniques, is examined in detail using transmission and scanning electron microscopy. Observations reveal that the precipitation of Nb3Al in a heavily dislocated Nb solid solution matrix initiates at grain boundaries and progresses along the 〈110〉 and 〈211〉 directions in the
Intermetallics, Apr 1, 2001
Boron-containing molybdenum silicides have been the focus of significant research of late due to ... more Boron-containing molybdenum silicides have been the focus of significant research of late due to their potentially superior lowtemperature ''pest'' resistance and high-temperature oxidation resistance comparable to that of MoSi 2 -based silicides; however, like many ordered intermetallics, they are plagued by poor ductility and toughness properties. Of the various multiphase Mo-Si-B intermetallic systems available, alloys with compositions of Mo-12Si-8.5B (at.%), which contain Mo, Mo 3 Si, and T2 phases, are anticipated to have higher toughnesses because of the presence of the relatively ductile Mo phase. In this study, we examine the ambient to high (1300 C) temperature fracture toughness (R-curve) and fatigue-crack growth characteristics of Mo-12Si-8.5B, with the objective of discerning the salient mechanisms governing crack growth. It is found that this alloy displays a relatively high intrinsic (crack-initiation) toughness at 800 up to 1200 C ($10 MPa p m), but only limited extrinsic R-curve (crack-growth) toughness. Although the lack of extrinsic toughening mechanisms is not necessarily beneficial to quasi-static properties, it does imply in a brittle material that it should show only minimal susceptibility to premature failure by fatigue, as is indeed observed at temperatures from ambient to 1300 C. Of particular significance is that both the fracture toughness and the threshold stress intensity for fatigue are increased with increasing temperature over this range. This remarkable property is related to a variety of toughening mechanisms that become active at elevated temperatures, specifically involving crack trapping by the a-Mo phase and extensive microcracking primarily in the Mo 5 SiB 2 phase. Published by Elsevier Science Ltd.
Solving the problem of solidification cracking during additive manufacturing of CrMnFeCoNi high-entropy alloys through addition of Cr3C2 particles to enhance microstructure and properties
Materials today advances, Jun 1, 2023
Response to Comment on “Cryoforged nanotwinned titanium with ultrahigh strength and ductility”
Science, May 13, 2022
We address the three main points of Guo et al . They claim that we should have used the engineeri... more We address the three main points of Guo et al . They claim that we should have used the engineering stress versus engineering strain curves to infer the mechanical properties of our nanotwinned titanium, question our sample design on the basis of a finite-element analysis, and doubt the immobility of some preexisting grain/twin boundaries in our electron backscatter diffraction micrographs. We find their analysis to be groundless and to contain many inconsistencies.
Scripta Materialia, Apr 1, 1998
Crack Growth in a ductile-phase-toughened in situ intermetallic composite under monotonic and cyclic loading
Scripta Metallurgica Et Materialia, Oct 1, 1993
One approach to improving the ductility and toughness of brittle solids is to incorporate a ducti... more One approach to improving the ductility and toughness of brittle solids is to incorporate a ductile phase into the brittle matrix in order to impede the extension of incipient cracks. In this regard, recent word has shown that niobium can provide significant ductile-phase toughening in several intermetallic composites via crack bridging, plastic stretching and interfacial debonding mechanisms; however, under cyclic loading the role of the ductile phase appears to be less effective. Accordingly, the purpose of the current study is to examine the effect of the addition of ductile Nb phase on fracture and fatigue behavior in an equiaxed Nb/Nb[sub 3]Al in situ composite; results are compared with behavior in unreinforced Nb[sub 3]Al and Nb to determine possible mechanisms of crack propagation in Nb-toughened Nb[sub 3]Al intermetallic composites.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, Jul 1, 2008
We present results from a systematic study linking material microstructure to monotonic and fatig... more We present results from a systematic study linking material microstructure to monotonic and fatigue properties of NiTi shape memory alloys. We consider Ni-rich materials that are either (1) hot rolled or (2) hot rolled and cold drawn. In addition to the two material processing routes, heat treatments are used to systematically alter material microstructure giving rise to a broad range of thermal, monotonic and cyclic properties. The strength and hardness of the austenite and martensite phases initially increase with mild heat treatment (300 • C), and subsequently decrease with increased aging temperature above 300 • C. This trend is consistent with transmission electron microscopy observed precipitation hardening in the hot-rolled material and precipitation hardening plus recovery and recrystallization in the cold-drawn materials. The low-cycle pseudoelastic fatigue properties of the NiTi materials generally improve with increasing material strength, although comparison across the two product forms demonstrates that higher measured flow strength does not assure superior resistance to pseudoelastic cyclic degradation. Fatigue crack growth rates in the hot-rolled material are relatively independent of heat treatment and demonstrate similar fatigue crack growth rates to other NiTi product forms; however, the cold-drawn material demonstrates fatigue threshold values some 5 times smaller than the hot-rolled material. The difference in the fatigue performance of hot-rolled and cold-drawn NiTi bars is attributed to significant residual stresses in the cold-drawn material, which amplify fatigue susceptibility despite superior measured monotonic properties.
Fatigue-crack propagation behavior in a high-carbon chromium SUJ2 bearing steel: Role of microstructure
International Journal of Fatigue, Mar 1, 2022
Composites Part B-engineering, Jun 1, 2021
For composite materials applied for energy absorption and vibration/noise reduction, it is of par... more For composite materials applied for energy absorption and vibration/noise reduction, it is of particular significance to clarify the role of strain rate and temperature on their mechanical properties. Here we present a study on the effects of strain rate (from 10 -3 s -1 to 1 s -1 ) and temperature (from room temperature to 350 • C) on the compressive properties of a 3-D printed Mg-NiTi interpenetrating-phase composite, which features high energy absorption efficiency and good damping capacity. Within the regimes of strain rate and temperature, the composite constantly exhibits a stable stress plateau on the stress-strain curves, yet displays markedly different damage mechanisms depending on the specific strain rate and temperature. The 3-D interpenetrating-phase architecture promotes an effective stress transfer in the composite and resists the propagation of local damages, thereby conferring a high strengthening efficiency and outstanding damage tolerance. The unique combination of mechanical properties makes the composite appealing for applications under various conditions, especially for absorbing mechanical energy and reducing vibrations and noise.
Stereophotogrammetric Investigation of Overload and Cyclic Fatigue Fracture Surface Morphologies in a Zr–Ti–Ni–Cu–Be Bulk Metallic Glass
Journal of Materials Research, Apr 1, 2000
Fracture surfaces of a recently developed Zr41.2Ti13.8Cu12.5Ni10.0Be22.5(at.%) bulk metallic glas... more Fracture surfaces of a recently developed Zr41.2Ti13.8Cu12.5Ni10.0Be22.5(at.%) bulk metallic glass were investigated using a three-dimensional surface reconstruction technique. Stereoscopic scanning electron microscopy of both fatigue and overload fracture surfaces permitted the creation of digital elevation models that were used to quantify important fracture surface features. Characterization of the surfaces revealed striations of nearly constant spacing on fatigue surfaces and a vein morphology characteristic in amorphous metals on the overload fracture surfaces. Additionally, at the onset of critical failure, crack-tip openings of ˜16 μm were observed that were consistent with measured values of fracture toughness. Interestingly, at the onset of fracture, deformation was confined to one side of the fracture plane, possibly because of the asymmetric emission of shear bands from the crack tip, consistent with the highly inhomogeneous nature of deformation in this alloy.
Philosophical Magazine A, Aug 1, 2000
This paper describes an alternative method for applying the Clausius-Clapeyron equation in a stud... more This paper describes an alternative method for applying the Clausius-Clapeyron equation in a study of the effect of temperature on the superelastic stress in the shape-memory alloy Nitinol-a candidate material for many medical devices, including in particular, endovascular stents. This new analysis will provide some clarification on the controversy regarding estimation of the thermodynamic equilibrium temperature. The theoretical uniaxial transformation strain has been calculated by means of the Clausius-Clapeyron equation. The calculated value of strain, 5.0%, corresponded closely with the experimentally measured value of 4.7%.
A damage-tolerant Ti-rich multiphase metallic-glass composite with hierarchically heterogeneous architecture
Composites Part B-engineering, Aug 1, 2023
Metallurgical and Materials Transactions, Mar 1, 1999
Structural heterogeneity governing deformability of metallic glass
Matter, Apr 1, 2023
Effect of local chemical order on the irradiation-induced defect evolution in CrCoNi medium-entropy alloy
Proceedings of the National Academy of Sciences
High- (and medium-) entropy alloys have emerged as potentially suitable structural materials for ... more High- (and medium-) entropy alloys have emerged as potentially suitable structural materials for nuclear applications, particularly as they appear to show promising irradiation resistance. Recent studies have provided evidence of the presence of local chemical order (LCO) as a salient feature of these complex concentrated solid-solution alloys. However, the influence of such LCO on their irradiation response has remained uncertain thus far. In this work, we combine ion irradiation experiments with large-scale atomistic simulations to reveal that the presence of chemical short-range order, developed as an early stage of LCO, slows down the formation and evolution of point defects in the equiatomic medium-entropy alloy CrCoNi during irradiation. In particular, the irradiation-induced vacancies and interstitials exhibit a smaller difference in their mobility, arising from a stronger effect of LCO in localizing interstitial diffusion. This effect promotes their recombination as the LCO ...
Zenodo (CERN European Organization for Nuclear Research), Mar 20, 2023
In situ high-temperature 3D imaging of the damage evolution in a SiC nuclear fuel cladding material
Materials & Design
Fracture processes in a coated SiC composite nuclear cladding material were found different at ro... more Fracture processes in a coated SiC composite nuclear cladding material were found different at room temperature and 1200°C. At both temperatures, cracking initiated in the outer monolithic SiC coating. The stress and strain when first coating crack occurred are much higher at 1200°C than room temperature. Typical crack toughening mechanisms occurred simultaneously in underlying composites upon load drops at both temperatures.
Uploads
Papers by Robert O Ritchie